Synchronous hysteresis motor

ABSTRACT

A synchronous hysteresis motor of the type including an internal stator and an overhung rotor having a hysteresis ring and rotatable with respect to the stator with a shaft rotatably mounted within the stator on two spaced apart bearing assemblies where the rear bearing assembly is spaced no more than A 0.225 H from the diametrical center of the hysteresis ring where H is the axial dimension of the rotor, and the ratio of the inside diameter of the ring to the outside diameter is at least 0.875.

United. States Patent- 1191 Weaver [11] 3,825,780 [4 1 July 23, 1974 SYNCHRONOUS HYSTERESIS MOTOR Inventor: Preston R. Weaver, Rocky Hill,

Conn.

Assigneez' UMC Electronics Company, North Haven, Conn.

Filed: I June 4, 1973 Appl. No.2 366,467

Related US. Application Data 1973, abandoned.

us. Cl...l 310/74, 310/164 1m. 01. H02k 7/02 [56] References Cited UNITED STATES PATENTS 10/1934 Haydon; 310/164 Continuation-impart of Ser. No. 320,061; Jan. 2, 7

Field of Search 310/51, 90,.154', 164, 74 5 2,140,365 12/1938 2,421,30l 5/1947 Swisher 2,509,583 5/1950 Youhouse 310/164 Primary ExaminerJ. D. Miller Assistant ExaminerRobert J. Hickey Attorney, Agent, or Firm-DeLio and Montgomery ABSTRACT A synchronous hysteresis motor of the type including an internal stator and an overhung rotor having a hysteresis ring and rotatablewith respect to the stator with ashaft rotatably mounted within the stator on two spaced apart bearing assemblies where the rear bearing'assembly is spaced no more than A 0.225 H from 'the diametrical center of the hysteresis ring v where H is the axial dimension of the rotor, and the ratio of the inside diameter of the ring to the outside diameter is at least 0.875.

2 Claims, 2 Drawing Figures Lenehan 3 10/ l 64 mmemzamn I A 3. 25.780

SHEET 10$ 2 1 SYNCHRONOUS HYSTERESIS MOTOR This application is a continuation-in-part of applicaring of such dimension and positioning to minimize intion Ser. No. 320,061 filed Jan. 2, 1973, now abandoned.

This invention relates to motors and more particularly relates to synchronous hysteresis motors.

A synchronous hysteresi's motor is one in which a rotor follows a rotating electrical field in synchronism therewith. The rotor requires a hard magnetic material with a high degree of hysteresis. Thus, as the magnetic field produced by the stator rotates .a magnetic pole created at the start of excitation persists on the'rotorlated to the power source frequency is essentially elimiv periphery opposite the stator axis. Rotation of the stator magnetic field creates a magnetic force between the t5 pole of the stator field and'tha't of the rotor resulting in a starting torque. Asthe rotor accelerates the hysteresis loss decreases increasing the power available for me- 1 chanical output at the shaft. Finally, at synchronous speed the hysteresis loss theoretically decreases to' zero and the magnetic axis of the rotor, stationary on the rotor periphery, lags the stator axis by; an angle proportional to the shaft load;

Such motors are quite often used in instrumentation and also for driving devicesat constant speeds such as recording or video tape drives, turntables, and the like.

Hysteresis motors may rotate at synchronous average.

speedsand still produce objectionable flutter, that is,

plications flywheels orthe-ir equivalent cannot be used to minimizethis effect. Another problem whichmay arise is vibration in the rotor that will be transmitted throughthe shaft and mount to the driv'en device.

The most'common-form of hysteresis motor is one inwhich the rotor is rotatably mounted between two bearings located in end bells and the stator surrounds the rotor, This produces a relatively large machine.

. In applications whereminimum depth of the motor with respect to length of shaft and maximum inertia are required, the rotoris'th'e outside member and includes variation in speed during each revolution. In many ap- 39 stantaneous variations in angular velocity of the rotor.

An object of this invention isto provide a new and improved hysteresis synchronous motor of the type described having a greaterratioof rotor diameter-todepth than heretofore possible.

Another object of this invention is to provide a motor of the type described in which vibration of the shaft renated.

Further objects of this invention-are to provide a motor of the type described with the required torque which has minimum instantaneous variations in angular velocity.

The features of the invention which are believed to be novel are set forth with particularity and distinctly claimed in the concluding portion of this application.

The invention, however,both as to its'operation and organization, together with further objects and advantages thereof may best be appreciated by reference to taken in conjunction the following detailed description with the drawings, in which:

tion; and

, FIG. 2 is a schematic diagram of the statorwinding.

*- FIG.'1 is an elevation of a motor, when mounted with the shaft axis ina horizontal plane, partly in half sec- Refeiringnow to the drawings, a motor lQembodying the invention comprises a stator 11 including laminations 12, windings 13 and a central support 14 having a bore '15 axially therethrough. The windings 13 are disposed in slots in laminations 'l2.and define therewith the poles of the stator. Member 14 .is adapted to be attached to a bracketor mount generally indicated at 16 ,in broken line. The stator is stationary.

A shaft 17 extends through bore 15 coaxially therewith. Shaft 17 is rotatably mounted with respect to staa ring of magnetic material within a carrying drum generally shaped in the .form of a cup. In this design the 'ra-' dial force on the rotor resulting from the rotating magnetic field will create a vibration on the shaft related to the power source frequency. Additionally, the bearings supporting the shaft must be sufficiently spaced to hold the run .out to an acceptable minimum. j

' The various parameters involved in the design of this type of motor have heretofore restricted efforts to minimize the depth of these motors with respect to thediameter thereof.

The present invention provides a new and improved synchronous hysteresis motor of thgty'pe having an outside or overhung rotor of minimum depth in relationv to diameten but with sufficient torque to serveits in; tended purpose. More specifically the present inventionpermits the provision of sucha motor having a diameter-to-depth ratio of two-to-one and greatenThe invention further provides such'a motorin which transient' variationin angularvelocity is minimized.

Briefly stated, the invention in one form thereof comprises a motor construction of the type described in which the axial dimension of the rotor is decreased reltor 11 by meansof first and second bearing assemblies 18 and 19; Each of bearing assemblies 18 and 19 comprises inner and outer races with roller or ball elements therebetw'een. Carried on shaft17 is a rotor member 20' in the shape of a cup overhanging the poles defined by laminations 12 and carrying therein a rotor ring 21 of f magnetic steel which spans the ends of laminations 12 i in the axial direction. Ring 21 is preferably of a No; 8l cobalt rnagnet steel" available'from' the Simonds Divi- 0 sion of Wallace-Murray Corporation, Lockport, N.Y. The cup 20 is of non-magnetic material such as aluminum. Ring 21 is coaxial with shaft 17 and rotatable therewith in rotor cup. 20.,The rotor cup has a dimen- I of ring 21. The rotor has an overall diameter D, and the ative to the diameter thereof by location of the rotorf' support bearings so that vibration-of the shaft is'essen-' tially eliminated and simultaneously providing a rotor motorhas an axial dimension of depth-T over a stator mounting surface 23 and the back of the rotor.

. It is the dimension A multiplied bylthe radial component of the magnetic force exerted, on the-rotor which will tend to produce vibrations in the rotor that-maybe transmitted to the shaft and mount to the drivendevice.

' The bearing assembly 18 for proper support of the shaft and rotor on the stator must be spaced a distance from bearing assembly 19 resulting in at least a portion of the bearing assembly 18 residing outsideof the plane of the outside edge of ring 21. The present invention may be best expressed after consideration of certain basic parameters of this type of motor.

The torque T on the shaft is T=la where' i l is the moment of inertia of the entire rotor and a is the angular acceleration of the rotor a dw/dt where w is the angular speed in radians 'dw T/I dt and in this type of rotor T= 11.3 N V A where N number of poles of motor V volume of hysteresis rotor ring v A,, area enclosed by hysteresis curve of rotor material As d approaches d the volume of the ring V approaches zero. As 1 approaches. 1,. (moment of inertia of rotor withoutring), the moment of inertia of the ring I, approaches zero. The torque also approaches iero.

The width or depth H of the rotor is effectively W where (A/l-l) 0 to 0.225 and ti /d 2 0.800 and N e 3.5 where A is the dimension between the diametrical center line of the ring, and the center of the rear bearing assembly 19 within rotor 20.

l have found that this disposition of the rear bearing assembly in relation to the diameter'and depth of the rotor minimizes any vibrations related to the frequency of the power source. The vibration transmitted to the output end of the shaft can be essentially eliminated when the dimension A is maintained in the range specified.

To minimize instantaneous changes in angular velocity, 1 can increase the air gapbetween the ring 21 and the periphery'of stator 11. This will decrease slot disturbances withoutaffecting the inertia of the rotor. To

compensate for the resultant decrease in torque due to increased air gap, the volume of the rotor may be increased within the limits specified. From equation (4),

which will provide a specified output of eleven ounce inches of torque at constant speed.

In the foregoing example, the dimension 1-1 included the slight extension of the open end of cup 20 beyond l(,'where W is the width of the ring and K is the dimen-.

sion from the end of the ring to the end of the rotor.

l have found that motors of the type described having a diameter-to-depth ratio D/l-l R of four or greater and a ratio D/T of two or greater, and having the desired operating characteristics may be provided if rotor ring 21 as shown in FIG. 1.

The overall depth of the motor (excluding shaft) from back ofthe cup to the mounting surface 23 of stator member 11 was 1.125 inches. The bearing assemblies, each having a dimension along the shaft of 0.281 inch, were spaced apart 0.385 inch between each other. The stator laminations had a thickness of 0.437 inch: FIG. 2 exemplifies the windings of stator 11. The windings comprise one or more main windings 30, and an equal number of starting windings 31. Both windings are connected to an AC source through terminals 32. A capacitance 33 is in circuit with the start windings for phase change. A directional reversing switch 34 is also provided.

It will thus be seen that the objects of the invention set forth as well as those made apparent from the foregoing description are efficiently attained. While preferred embodiments of the invention have been set forth for purposes of disclosure, modification to the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.

What is claimed is: 1

1. A hysteresis synchronous motor of the type comprising a stator member including a plurality of radially extending laminations having windings thereon, a bore coaxially definedin said stator member, a shaft extending through said bore coaxial with said stator member, a generally cup-shaped rotor member on said shaft and overhanging said stator and having a dimension along line perpendicular to said shaft essentially corresponding with the center line of said stator laminations, first andsecond spaced apart bearing assemblies in said stator bore rotatably mounting said shaft, one of said bearing assemblies being positioned in saidbore on the side where of said ring diametrical center line toward the open end of said cup-shaped rotor, the other of said bearing assemblies having a center line which is spaced from the diametrical center line of said ring on the side thereof opposite said one bearing'assembly by a distance A 1 where (A/H) 0 to .225 and r 2. The motor of claim 1 wherein said stator member has a mounting surface and a dimension from said a mounting to the end-of said cup-shaped rotor of T, said rotor member has an overall diameter of D, and (WT) 2.

,i*z2;e8? M W T T J HCE. ERTI I TE OFQCORRECTION} a n 3,"8 2, 7'80 1 fn g July 23-, 1974 lhve rg) Preston R. weaver It is certified that erroreppeai i in gthe above-identified patent v and that said Letters Patent are. hereby eq'rrected as shown below:

. I. j Q d Column 4, line 34; "d Should e 2 Sigh ed and'eealedtthisg8th de' y October 1974 (SEAL) Attestzfl MCCOY M. GIBSON JR. 5 c, MARSHALL *DANN V v Attesting Officer T 1 f Commissioner of Patents 13 v v I 'UNITEDISTATES. PATENT OF CERTIFICATE OF CORRECTION Pater 1t No. I 5 v V m July. 23', 1974 Inv t r(g) Preston R. Weaver v It is certified that error ap'pears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 34,- "d ho l read d Si n-ed ahdissaled .this 8th 'dey of October 1974 (SEAL) Attest: I

MCCOY M. GIBSON JR. c c. MARSHALL 'DANN v Attesting Officer Commissioner of Patents 

1. A hysteresis synchronous motor of the type comprising a stator member including a plurality of radially extending laminations having windings thereon, a bore coaxially defined in said stator member, a shaft extending through said bore coaxial with said stator member, a generally cup-shaped rotor member on said shaft and overhanging said stator and having a dimension along said shaft of H, a ring member of magnetic material carried by said cup-shaped member coaxial with and radially outwardly of said stator laminations, said ring member having an inside diameter d1, an outside diameter d2 and a continuous cylindrical inner surface defined on said inside diameter, said ring having a center line perpendicular to said shaft essentially corresponding with the center line of said stator laminations, first and second spaced apart bearing assemblies in said stator bore rotatably mounting said shaft, one of said bearing assemblies being positioned in said bore on the side of said ring diametrical center line toward the open end of said cup-shaped rotor, the other of said bearing assemblies having a center line which is spaced from the diametrical center line of said ring on the side thereof opposite said one bearing assembly by a distance A where N (d1/d2)/(A/H) where N > OR = 3.5 and (A/H) 0 to .225 and d1/d2 > OR = 0.875.
 2. The motor of claim 1 wherein said stator member has a mounting surface and a dimension from said mounting to the end of said cup-shaped rotor of T, said rotor member has an overall diameter of D, and (D/T) >
 2. 